Wire Feeder With Non-Linear Speed Control

ABSTRACT

A welding machine with a wire feeder and a controller is disclosed. The wire feeder includes a wire feed motor with a motor speed input. The controller is coupled to the motor speed control input. A user selectable wire feed speed input is also connected to the controller. The controller has an input circuit coupled with a non-linear stage such that the relationship between the user selectable wire feed speed input and the actual wire feed speed is not linear. The selectable input may be a potentiometer mounted on a front panel as the user selectable wire feed speed input. The non-linearity may be continuous or two discrete gains.

FIELD OF THE INVENTION

The application relates generally to electrode wire feeders used inwelding, and, more particularly, to a wire feed speed controller forwire feeders used in welding.

BACKGROUND OF THE INVENTION

Many welding applications such as MIG (metal inert gas) or GMAW (gasmetal arc welding) utilize a wire feeder to provide filler metal to theweld. Generally, the wire feeder will provide wire at a nominallyconstant speed (typically given in inches per minute). Wire feed speedcontrollers control the speed at which the wire is fed to the arc.

A typical prior art wire feeder includes a motor that pulls wire from areel and feeds the wire to the weld arc. The motor is controlled by awire feed controller that may be a stand alone controller or maybe partof a controller that controls other aspects of the welding process. Thewire feed controller controls the speed of the wire feeder and typicallyincludes a potentiometer on a front panel of the controller which theuser uses to set wire feed speed.

A user selectable input, such as the angular position of a knob,typically determines the resistance of the potentiometer, which is usedto set the speed point in the control circuit. The controller mayinclude feedback circuitry to control the wire feed speed, or the speedcontrol may be open loop.

The operator control panel label typically includes markings for theknob that indicate a percent of the maximum wire feed speed. The userselects the desired percentage of maximum wire feed speed. For example,at 100 percent, the wire feeder will operate at top speed, and at 50percent the wire feeder will operate at one-half of its top speed. Wirefeeder and welding machine user's manuals often include tables thatindicate the percent setting on the potentiometer (knob) for variousgauge (thickness) materials to be welded. Generally, lesser gaugematerial requires the wire be fed at a slower speed. A typical range forwire feed speeds is from 50 inches per minute for thinner material to650 inches per minute for thicker material.

These,controls are simple and easy to implement. However, they have asignificant drawback. Specifically, the potentiometer is substantiallylinear: the relationship between changes in angular position and changesin wire feed speed is linear over the entire range. For example, if theentire,range of wire feed speed is 600 inches per minute, and the totalangular rotation 300 angular degrees, then two percent of the angularrange (6 angular degrees) will will result in 12 inches per minutedifference in wire feed speed.

The sensitivity (inches/minute/degree of angular rotation) is determinedby the relationship between angular position and wire feed speed. Thus,the precision by which wire feed speeds may be operated selected is thesame at the fast and slow end of the wire feed speed range.

However, when welding, the speed selection at the faster end of wirefeed speed range (heavier gauge material) need not be as precise as thespeed selection at the slower end of the wire feed speed range. Forexample, when operating at 600 inches per minute, being off by 5 or 10inches per minute may not be significant. However, when operating at 50inches per minute, being off by 5 or 10 inches per minute may be verysignificant and can confuse the operator since 175 inches/minute isavailable on both toggle switch positions. Thus, it is desirable thatthe control be more precise at slower wire speed feeds than at fasterwire feed speeds.

Some prior art wire feed controllers overcame this drawback by providinga toggle switch to select between a faster range and a slower range.Thus, the angular sensitivity at slower speeds is greater than whenusing the potentiometer for the full range. However, this requires anadditional control switch. Also, this prevented the use of a direct wirefeed speed reading, since a single potentiometer knob was used formultiple wire feed speed ranges.

FIG. 1 is part of a panel of such a prior art wire feed control having atwo-range speed control. Two control knobs are shown on this portion ofthe panel. Control knob 101 controls the wire speed feed, and controlknob 103 controls the output voltage (and is not particularly relevantto the present invention). Control knob 101 is part of a potentiometerwhich has an output provided to a controller.

A switch 102 selects between the fast and slow range of wire feedspeeds. Specifically, when switch 102 is toggled to the left, the slowrange (between 50 and 350 inches per minute) is selected. When switch102 is toggled to the right, the full range (50 to 650 inches perminute) is selected. Thus, to select 175 inches per minute the userwould toggle switch 102 to the left and select 50 percent on knob 101.This would provide 50 percent of the maximum (350) or 175 inches perminute. Should the user desire a wire feed speed of about 490 inches perminute switch 102 would be toggled to the right and the setting for knob101 would be about 75 percent. This would provide approximately 490inches per minute. However, this sort of design does not allow the wirefeed speed to be displayed in inches per minute on the selector knob.Additionally, this does not allow the user to effectively access allwire feeds speeds over the entire range, without toggling a switch.

Experienced welders will often know the wire feed speed necessary forthe weld they are performing. Also, inexperienced welders can easily thenecessary wire feed speed determine using a table or slide rulecalculator. However, given the prior art wire feed speed control (whichrequired the panel to show percent of maximum wire feed speed) even anexperienced welder needed to consult the user's manual.

Another prior art wire feed controller is part of the Miller™ RCSP-45(Remote Control Synergic Pulser) used for pulse MIG arc welding. Thiscontroller is complex and expensive and has tow adjustment knobs: arcpower and arc length. Neither knob directly controlled wire feed speed,although wire feed speed was determined based on the arc length and arcpower selected. As used herein, a parameter is directly controlled whena selectable input—such as a knob on the operator panel—is used tocontrol the parameter directly, rather than indirectly by altering otheroutput parameters. The indirect control effected a non-linear change inwire feed speed for changes in arc length and arc power. However, thisprior art did not allow independent control of the wire feed speed by asingle knob.

Accordingly, it would be desirable to provide a wire feeder thatprovided an independent control of wire feed speed which was non-linearover the range of wire feed speeds. Additionally, the control should besuch that the user may read the control in inches per minute, ratherthan percent of maximum speed.

SUMMARY OF THE PRESENT INVENTION

A first aspect of the invention is a wire feeder that, feeds wire to aweld at a controllable rate. The wire feeder includes a wire feed motorwith a motor speed input. A controller is coupled to the motor speedcontrol input. A user selectable wire feed speed input is also connectedto the controller. The controller has an input circuit coupled with anon-linear stage such that the relationship between the user selectablewire feed speed input and the actual wire feed speed is not linear.

An alternative embodiment is using a potentiometer mounted on a frontpanel as the user selectable wire feed speed input. Another alternativeis to directly and independently control the wire feed speed.

Another alternative using a gain stage having a first gain over a firstrange of inputs and a second gain over a second range of inputs tocreate the non-linearity. An alternative uses a gain stage having avarying gain to provide a gradually changing gain over the range of wirefeed speeds.

Alternative embodiments includes having just a controller, a controllerwith a wire feeder, or an entire welding machine.

Other principal features and advantages of the invention will becomeapparent to those skilled in the art upon review of the followingdrawings, the detailed description and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is part of a front panel layout of a prior art wire feed speedcontroller;

FIG. 2 is a part of a front panel layout of a wire feed speed controllerthat implements the present invention; and

FIG. 3 is a circuit diagram used to implement part of the wire feedspeed controller of the present invention.

Before explaining at least one embodiment of the invention in detail itis to be understood that the invention is not limited to the details ofconstruction and the arrangement of the components set forth in thefollowing description or illustrated in the drawings. The invention iscapable of other embodiments or of being practiced or carried out invarious ways. Also, it is to be understood that the phraseology andterminology employed herein is for the purpose of description and shouldnot be regarded as limiting. Like reference numerals are used toindicate like components.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

While the present invention will be illustrated with reference to aparticular front panel arrangement and a particular circuit diagram itshould be understood at the outset that the wire feed speed control maybe implemented with other components and lay-outs.

Generally, the present invention provides for a non-linear output of thewire feed speed control knob, The non-linear output voltage allows forgreater sensitivity (per angular unit) at slower wire feed speeds, andlesser sensitivity (per angular unit) at faster wire feed speeds. Thisallows the wire feed speed to be displayed in inches per minute, andallows the user to effectively select a wire feed speed over an entirerange using a single potentiometer, without toggling a range switch.

FIG. 2 shows a portion of a front panel of a wire feed speed controller(that corresponding to the portion of a prior art panel in FIG. 1)implementing the present invention. The wire feed speed is set using aknob 202 and has range of 50 to 700 inches per minute. However, it maybe easily seen that the slower end of the wire feed speed has a moresensitive control. For example, the angular difference of 100 inches perminute between 50 and 150 inches per minute is much greater than theangular difference of 100 inches per minute between 600 and 700 inchesper minute. Thus, the user may select a desired wire feed speeddirectly. The non-linear control allows inches per minute to bedisplayed rather than percent of maximum wire feed speed. Also, the usermay effectively select the wire feed speed, even at slow speeds, becausethe sensitivity is lower at low speeds.

An input circuit which implements the invention is shown in FIG. 3 andincludes resistors R1-R8, an op amp A1, a capacitor C1, and a zenerdiode DZ1. Resistor R1 is the wire feed speed control potentiometermounted on the front panel of the controller, and is adjusted using knob202. The resistance of potentiometer R1 varies from 0 ohms to 1K ohms,depending upon the angular position of knob 101. nResistors R3 (562ohms) and R4 (100 ohms) connect potentiometer R1 to a +10V voltagesource and ground. The resistances of resistors R3 and R4 are selectedto set the minimum and maximum voltages that the output resistor of R1can provide. Resistor R5 (100K ohms), resistor R6 (200K ohms) andcapacitor C1 (0.0047 μF) form a voltage divider and an input filter forthe non-inverting input of op amp A1. Thus, the voltage from the +10volt source, modified by the setting of potentiometer R1 and divided byresistors R3 and R4, is provided to the non-inverting input of op amp A1through resistor R5.

Resistor R7 (6.82K ohms) and zener diode DZ1 (3.0 zener voltage), alongwith resistor R8 (10K ohms) form a non-linear gain network (thatimplements the non-linearity of wire feed speed relative to the angularposition of knob 202) and are connected to the inverting input of op ampA1. The output voltage of op amp A1, V0, is given byV0=VI+(R8/R7)*(VI−VZ) when VI is greater than VZ, or V0=VI when VI isless than or equal to VZ. Thus, it may be seen that the output of op ampA1 will depend upon the setting of potentiometer R1, but will not varylinearally with the setting of potentiometer of R1.

The output of op amp A1, V0, is provided to the controller which uses itto set the wire feed speed. The wire is fed by a wire feed motor, whichhas a speed control input from the controller. This embodiment providestwo discrete sensitivities, one when VI<VZ, and one when VI<=VZ. Otheralternatives include a greater number of sensitivities or a graduallychanging sensitivity.

The preferred embodiment uses the output of op amp A1 as the input to aPWM chip (UC 3524 e.g.) and then modulates a voltage (i.e. a wire feedspeed input) applied to a dc permanent magnet motor. The speed of themotor is dependent on the average modulated voltage applied thereto.Other motor controllers can be used to implement this invention. Onealternative provides non-linearities in the wire feed motor becompensated for by the input circuit. Another alternative provides fordepressing a button or rotating a wheel for the selectable input.

The controller may be a stand alone unit, part of the controller for thewelding machine, or an add on. The total package may include a weldingpower supply in the same or a separate-ease as the controller, or a wirefeeder in a case with the controller, or each component having its owncase.

Numerous modifications may be made to the present invention which stillfall within the intended scope hereof. Thus, it should be apparent thatthere has been provided in accordance with the present invention amethod and apparatus for controlling a wire feeder that fully satisfiesthe objectives and advantages set forth above. Although the inventionhas been described in conjunction with specific embodiments thereof, itis evident that many alternatives, modifications and variations will beapparent to those skilled in the art. Accordingly, it is intended toembrace all such alternatives, modifications and variations that fallwithin the spirit and broad scope of the appended claims.

1.-5. (canceled)
 6. An apparatus for feeding wire at a controllable wirefeed speed to a weld comprising: a wire feed motor, having a wire feedspeed; a controller means for controlling the motor speed, wherein thecontroller means is coupled to the motor; and an input means forallowing a user to select a wire feed speed; wherein the controllermeans includes an input circuit coupled to the input means, and whereinthe input circuit includes non-linear means for creating a non-linearrelationship between a setting of the input means and the wire feedspeed.
 6. (canceled)
 7. The apparatus of claim 6 where the input circuitincludes a gain stage means for providing at least two gains.
 8. Theapparatus of claim 6 wherein the non-linear means includes a gain stagemeans for providing a varying gain.
 9. A method of controlling wirefeeder comprising the steps of: providing the wire at a controlledspeed; providing a user input; and creating a non-linear relationshipbetween the user input and the wire feed speed.
 10. The method of claim9 wherein the step of providing a user input includes providing apotentiometer mounted on a front panel.
 11. The method of claim 10 wherethe step of creating includes the step of providing at least two gainsin a gain stage connected to the user input.
 12. An apparatus forcontrolling the rate at which wire is fed to a weld, comprising: a wirefeed motor output; a selectable wire feed speed input; and an inputcircuit coupled to the selectable wire feed speed input, and wherein theinput circuit includes a non-linear stage such that the relationshipbetween the selectable wire feed speed input and the wire feed output isnot linear.
 13. The apparatus of claim 12 wherein the selectable wirefeed speed input includes a potentiometer mounted on a front panel. 14.The apparatus of claim 13 where the input circuit includes a pluralityof gain stages each having gain over one of a plurality of input ranges.15. The apparatus of claim 13 wherein the non-linear stage includes again stage having a varying gain.
 16. The apparatus of claim 12 whereinthe controller directly controls wire feed speed.
 17. An apparatus forcontrolling the rate at which wire is fed to a weld comprising: a wirefeed motor output, corresponding to a wired feed speed; controller meansfor controlling the motor speed, wherein the controller means is coupledto the motor output; and an input means for allowing a user to select awire feed speed; wherein the controller means includes an input circuitcoupled to the input means, and wherein the input circuit includesnon-linear means for creating a non-linear relationship between asetting of the input means and the motor output.
 18. The apparatus ofclaim 17 wherein the input means includes a potentiometer mounted on afront panel.
 19. The apparatus of claim 18 where the input circuitincludes a gain stage means for providing at least two gains.
 20. Theapparatus of claim 18 wherein the non-linear means includes a gain stagemeans for providing a varying gain.
 21. An apparatus for arc weldingcomprising: a welding power supply connected to provide welding power tothe arc; a wire feed motor, disposed to provide wire to the arc andhaving a wire feed speed; a controller, coupled to the wire feed motor;and a selectable wire feed speed input; wherein the controller includesan input circuit coupled to the selectable wire feed speed input, andwherein the input circuit includes a non-linear stage such that therelationship between the selectable wire feed speed input and the wirefeed speed is not linear.
 22. The apparatus of claim 21 wherein theselectable wire feed speed input includes a potentiometer mounted on afront panel.
 23. The apparatus of claim 22 where the input circuitincludes a plurality of gain stages each having gain over one of aplurality of input ranges.
 24. The apparatus of claim 22 wherein thenon-linear stage includes a gain stage having a varying gain.
 25. Theapparatus of claim 21 wherein the controller directly controls wire feedspeed.
 26. The apparatus of claim 5 wherein the input means includes apotentiometer mounted on a front panel.